That would be fine in simply "Game of the Generation" which could take popularity, influence, quality, etc into account, but since you specifically state "Best Game of the Generation", no way is COD ahead of the likes of Mass Effect, Uncharted, Red Dead Redemption, GTA, Bioshock and Fallout 3.

Modern Warfare, for better or worse, influenced the industry in such a massive way that we're still getting the aftershock. Battlefield 2 introduced many of those aspects before MW, but MW gets the credit. Also, it was pretty freakin' awesome. The campaign and the multi-player were top-notch!